docs: update patch testing instructions

[jsjoeio]

• docs: explain how to test exec-argv
• docs: update heartbeat.diff testing
• Revert "docs: update heartbeat.diff testing"
• docs: explain how to test telemetry patch

[github-actions]

✨ code-server dev build published to npm for PR #5543!

• Last publish status: success
• Commit: 88f8812

To install in a local project, run:

npm install @coder/code-server-pr@5543

To install globally, run:

npm install -g @coder/code-server-pr@5543

[codecov]

Codecov Report

Merging #5543 (88f8812) into main (b486354) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5543   +/-   ##
=======================================
  Coverage   72.44%   72.44%           
=======================================
  Files          30       30           
  Lines        1673     1673           
  Branches      366      366           
=======================================
  Hits         1212     1212           
  Misses        398      398           
  Partials       63       63           

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